1. Field of the Invention
The present invention relates to a golf ball with a dimple pattern on its surface. More specifically, the present invention relates to a dimple pattern for a golf ball where each dimple has a curvature continuity at the entry radius, the inflection point and the center point at the bottom of the dimple.
2. Description of the Related Art
Golfers realized perhaps as early as the 1800's that golf balls with indented surfaces flew better than those with smooth surfaces. Hand-hammered gutta-percha golf balls could be purchased at least by the 1860's, and golf balls with brambles (bumps rather than dents) were in style from the late 1800's to 1908. In 1908, an Englishman, William Taylor, received a patent for a golf ball with indentations (dimples) that flew better ad more accurately than golf balls with brambles. A.G. Spalding & Bros., purchased the U.S. rights to the patent and introduced the GLORY ball featuring the TAYLOR dimples. Until the 1970s, the GLORY ball, and most other golf balls with dimples had 336 dimples of the same size using the same pattern, the ATTI pattern. The ATTI pattern was an octohedron pattern, split into eight concentric straight line rows, which was named after the main producer of molds for golf balls.
The only innovation related to the surface of a golf ball during this sixty year period came from Albert Penfold who invented a mesh-pattern golf ball for Dunlop. This pattern was invented in 1912 and was accepted until the 1930's.
In the 1970's, dimple pattern innovations appeared from the major golf ball manufacturers. In 1973, Titleist introduced an icosahedron pattern which divides the golf ball into twenty triangular regions. An icosahedron pattern was disclosed in British Patent Number 377,354 to John Vernon Pugh, however, this pattern had dimples lying on the equator of the golf ball which is typically the parting line of the mold for the golf ball. Nevertheless, the icosahedron pattern has become the dominant pattern on golf balls today.
In the late 1970s and the 1980's the mathematicians of the major golf ball manufacturers focused their intention on increasing the dimpled surface area (the area covered by dimples) of a golf ball. The dimpled surface for the ATTI pattern golf balls was approximately 50%. In the 1970's, the dimpled surface area increased to greater than 60% of the surface of a golf ball. Further breakthroughs increased the dimpled surface area to over 70%. U.S. Pat. No. 4,949,976 to William Gobush discloses a golf ball with 78% dimple coverage with up to 422 dimples. The 1990's have seen the dimple surface area break into the 80% coverage.
The number of different dimples on a golf ball surface has also increased with the surface area coverage. The ATTI pattern disclosed a dimple pattern with only one size of dimple. The number of different types of dimples increased, with three different types of dimples becoming the preferred number of different types of dimples. U.S. Pat. No. 4,463 to Oka et al., discloses a dimple pattern with four different types of dimples on surface where the non-dimpled surface cannot contain an additional dimple. United Kingdom patent application number 2157959, to Steven Aoyama, discloses dimples with five different diameters. Further, William Gobush invented a cuboctahedron pattern that has dimples with eleven different diameters. See 500 Year of Golf Balls, Antique Trade Books, page 189. However, inventing dimple patterns with multiple dimples for a golf ball only has value if such a golf ball is commercialized and available for the typical golfer to play.
Additionally, dimple patterns have been based on the sectional shapes, such as octahedron, dodecahedron and icosahedron pstterns. U.S. Pat. No. 5,201,522 discloses a golf ball dimple pattern having pentagonal formations with equally number of dimples therein. U.S. Pat. No. 4,880,241 discloses a golf ball dimple pattern having a modified icosahedron pattern wherein small triangular sections lie along the equator to provide a dimple-free equator.
To further enhance aerodynamics for the flight of a golf ball, the designs of the dimples have been studied and improved upon by the golf industry. For example, Shimosaka et al., U.S. Pat. No. 5,720,676 for a Golf Ball, discloses a cross-sectional area of each dimple that is equal 0.01 mm below the dimple edge. The dimples of the Shimoska patent have an equivalent cross-section below this level since the edges of the dimples above 0.01 mm are rounded after painting thereby departing from a master's reverse dimple pattern.
Another example is Ihara et al, U.S. Pat. No. 4,840,381, for a Golf Ball, and Yamagishi et al., U.S. Pat. No. 5,752,889, for a Two-Piece Solid Golf Ball, both of which disclose a gentle transition over the edge portion of each dimple. The Ihara and Yamagishi patents are particularly directed at a golf ball with a cover composed of an ionomer material.
Yet another example is Kasashima et al., U.S. Pat. No. 5,906,551 for a Golf Ball, which discloses having dimples on the parting line. The dimples on the parting line have an entry angle that is greater than dimples that do not lie on the parting line. The use of a larger entry angle for parting line dimples in the Kasashima patent is to improve the symmetry.
Another example of entry angles of dimples is disclosed in Miyagawa et al, U.S. Pat. No. 5,857,924, for a Golf Ball. The Miyagawa patent has the entry angle between 5 and 20 degrees in order to prevent lowering of the spin susceptibility due to repetitive hits.
Another example of manipulation of the edge of a dimple is disclosed in Oka, et al., U.S. Pat. No. 4,813,677, for a Golf Ball. The Oka patent has a sharp inclination for the dimple wall surface to increase the volume of the dimple.
A departure from gradual dimples edges is disclosed in Boehm, U.S. Pat. No. 5,566,943 for a Golf Ball. The Boehm patent discloses dimples that have a constant depth for the entire dimple area. Essentially, the side wall of the dimple of the Boehm patent is at a 90 degree angle to the surface which should improve resistance to hits with an iron.
Although there are hundreds of published patents related to golf ball dimples, there still remains a need to improve upon current dimples, particularly for golf balls with thermoset polyurethane covers. Golf balls with thermoset polyurethane covers such as the Maxfli REVOLUTION, the Maxfli HT, the Titleist PROFESSIONAL, the Titleist TOUR PRESTIGE, and the Slazenger RAM 420 all need to compensate for the inherent properties of the polyurethane material which prevents the use of certain manufacturing techniques available to covers composed of ionomer materials such as roto-finishing. One example to overcome this problem is a dual radius design such as disclosed in Moriyama, U.S. Pat. No. 5,735,757. However, there is still a need for a dimple designed to maximize the aerodynamics of a golf ball with a thermoset polyurethane cover.